I don’t think “supposed to happen” factors into evolution. It’s just a solution to a problem we created. If you think we shouldn’t kill them, don’t you think we shouldn’t have put them there in the first place? It’d be one thing if they spread everywhere naturally, but we put them there. Besides, who doesn’t want to…

It’s called fantasy for a reason. There’s no reason to dislike ideas simply because they aren’t realistic. The point of fantasy is that it isn’t real, and thus things that don’t happen in real life happen far more often.